and is a primitive that can be used to combine two true-or-false statements, known as booleans in the computer world, into a single true-or-false statement such that the result is true if and only if both inputs are true. For instance, if we wanted a turtle to eat if (A) they were hungry and (B) if there was food in their patch, we could say:

if hungry? and food-here? [
  eat
]

In this model, we use and to generate a river down the middle of our world. a patch turns blue if and only if its x coordinate is both to the left of (width / 2) and to the right of - (width / 2), otherwise, it remains a green patch.